Catalytic Gas Phase Fluorination of 1233xf to 1234yf

ABSTRACT

The present invention provides a process for preparing 1234yf, comprising:
         (i) contacting 1233xf with hydrogen fluoride HF in gas phase in the presence of a fluorination catalyst under conditions sufficient to produce a reaction mixture;   (ii) separating the reaction mixture into a first stream comprising HCl, 1234yf and a second stream comprising HF, unreacted 1233xf and 245cb;   (iii) recycling at least a part of the second stream at least in part back to step (i).       

     The present invention also provides a process for preparing 1234yf, comprising:
         (i) contacting 1233xf with hydrogen fluoride HF in gas phase in the presence of a fluorination catalyst under conditions sufficient to produce a reaction mixture;   (ii) separating the reaction mixture into HCl and a stream containing the fluorinated products;   (iii) separating said stream containing the fluorinated products into a first stream comprising 1234yf and a second stream comprising HF, unreacted 1233xf and 245cb;   (iv) recycling at least a part of the second stream at least in part back to step (i).

FIELD OF THE INVENTION

The present invention relates to the gas phase catalyzed fluorination of2-chloro-3,3,3-trifluoro-1-propene (1233xf) to produce2,2,2,3-tetrafluoropropene (1234yf). More particularly, the presentinvention relates to processes wherein 1233xf; optionally containing alow level of polymerization inhibitor, is contacted with hydrogenfluoride (HF) in a gas phase reaction, in the presence of a fluorinationcatalyst to produce 1234yf. The desired product, 1234yf is known to haveutility as a foam blowing agent, refrigerant, aerosol propellant, heattransfer media, fire extinguisher, etc. Furthermore, 1234yf is known tohave zero Ozone Depletion Potential (ODP) and very low Global WarmingPotential (GWP) of much less than 150.

BACKGROUND OF THE INVENTION

The Montreal Protocol for the protection of the ozone layer mandated thephase out of the use of chlorofluorocarbons (CFCs). Materials more“friendly” to the ozone layer, such as hydrofluorocarbons (HFCs) e.g.HFC-134a replaced chlorofluorocarbons. The latter compounds have provento be green house gases, causing global warming and were regulated bythe Kyoto Protocol on Climate Change. With the continued concern overglobal climate change there is an increasing need to developtechnologies to replace those with high ozone depletion potential (ODP)and high global warming potential (GWP). Though hydrofluorocarbons(HFCs), being non-ozone depleting compounds, have been identified asalternatives to chlorofluorocarbons (CFCs) and hydrochloro-fluorocarbons(HCFCs) as solvents, cleaning agents and heat transfer fluids, theystill tend to have significant GWP. Hydrofluoroolefins (HFO) have beenidentified as potential alternatives with zero ODP and low GWP.

Hence, numerous documents have provided such HFOs.

Methods of preparing hydrofluoroalkenes are known. For example, WO2007/079431 discloses processes for the production of fluorinatedolefins, including hydrofluoropropenes. The processes which are broadlydescribed as a single reaction or two or more reactions involvefluorination of compound of the formula C(X)_(m)CCl(Y)_(n)C(X)_(m) to atleast one compound of formula CF₂CF═CHZ, where each X, Y and Z isindependently H, F, Cl, I or Br and each m is independently 1, 2 or 3and n is 0 or 1. 1234yf is prepared by fluorinating 1233xf into1,1,1,2-tetrafluoro-2-chloropropane (HFC244bb), followed bydehydrochlorination. 1233xf is prepared by trifluorination of thecorresponding chlorinated precursor (CCl₂═CClCH₂Cl).

EP-A-939071 discloses, among many possibilities, gas-phase fluorinationof an halogenated propene (according to a very long list) into afluorinated propene (including in the list 1234yf).

WO 2008/054781 discloses a variety of processes for producing a varietyof fluoropropanes and halofluoropropenes by reacting halopropanes orhalopropenes with HF optionally in the presence of a catalyst. Itdiscloses a process for making 1234yf by reacting2,3-dichloro-1,1,1-trifluoropropane (243 db) in the presence of HF, on acatalyst, especially Cr/Co 98/2. Reaction products comprise 1234yf and2-chloro-3,3,3-trifluoro-1-propene (1233xf), the latter being the mainproduct; other products being 1-chloro-3,3,3-trifluoro-1-propene(1233zd) as well as 245cb and 1234ze which are also formed.

WO 2008/002500 discloses a process for making a mixture of2,3,3,3-tetrafluoro-1-propene (HFO 1234yf) and1,3,3,3-tetrafluoro-1-propene (HFO 1234ze) by catalytic conversion of1,1,1,2,3-pentafluoropropane (HFC 245eb) on a dehydrofluorinationcatalyst.

WO 2008/040969 discloses a process comprising dehydrochlorination of 243db into 1233 (xf as well as zd), followed by a reaction involvingformation of 1,1,1,2-tetrafluoro-2-chloropropane (244bb) and laterformation of the desired 2,3,3,3-tetrafluoro-1-propene throughdehydrochlorination. Example 1 of said document discloses a gas phasereaction at atmospheric pressure of 243 db with HF on a Zn/chromiacatalyst, whereby 1234yf and 1233xf are formed, together with a smallamount of 245cb. Example 2 of said document discloses a gas phasereaction at atmospheric pressure of 245cb in presence of HF on the samecatalyst (contact time 5 sec) whereby 1234yf is formed.

WO 2009/015317 discloses the reaction of a chlorinated compound whichcan be 1,1,2,3-tetrachloro-1-propene (1230xa),1,1,1,2,3-pentachloropropane (240 db) or 2,3,3,3-tetrachloro-1-propene(1230xf) with HF, in gas phase, on a catalyst and in the presence of atleast one stabilizer. This process allows obtaining2-Chloro-3,3,3-trifluoro-1-propene (1233xf).

US 2009/0240090 discloses a process for making2,3,3,3-tetrafluoro-1-propene (1234yf) starting from a compound offormula (I) CX₂═CClCH₂X, or formula (II) CX₃CCl═CH₂ or formula (III)CX₃CHClCH₂X with X═F, Cl, Br, I. The process comprises three steps,which can be followed by purification. The process includes recyclingsteps allowing higher conversions and yields.

SUMMARY OF THE INVENTION

The present invention provides a process for preparing2,2,2,3-tetrafluoropropene (1234yf), comprising:

-   -   (i) contacting 2-chloro-3,3,3-trifluoro-1-propene (1233xf) with        hydrogen fluoride HF in gas phase in the presence of a        fluorination catalyst under conditions sufficient to produce a        reaction mixture;    -   (ii) separating the reaction mixture into a first stream        comprising HCl, 2,2,2,3-tetrafluoropropene (1234yf) and a second        stream comprising HF, unreacted        2-chloro-3,3,3-trifluoro-1-propene (1233xf) and        1,1,1,2,2-pentafluoropropane (245cb);    -   (iii) recycling at least a part of the second stream at least in        part back to step (i).

In one embodiment, the first stream is further separated into HCl and2,2,2,3-tetrafluoropropene (1234yf), preferably in a distillation step.

The present invention also provides a process for preparing2,2,2,3-tetrafluoropropene (1234yf), comprising:

-   -   (i) contacting 2-chloro-3,3,3-trifluoro-1-propene (1233xf) with        hydrogen fluoride HF in gas phase in the presence of a        fluorination catalyst under conditions sufficient to produce a        reaction mixture;    -   (ii) separating the reaction mixture into HCl and a stream        containing the fluorinated products;    -   (iii) separating said stream containing the fluorinated products        into a first stream comprising 2,2,2,3-tetrafluoropropene        (1234yf) and a second stream comprising HF, unreacted        2-chloro-3,3,3-trifluoro-1-propene (1233xf) and        1,1,1,2,2-pentafluoropropane (245cb);    -   (iv) recycling at least a part of the second stream at least in        part back to step (i).

Embodiments are the following:

-   -   the reaction mixture obtained at step (i) comprises        2,2,2,3-tetrafluoropropene (1234yf) and        1,1,1,2,2-pentafluoropropane (245cb) in a molar ratio of 1:5 to        3:1, preferably 1:4 to 2:1.    -   the reaction mixture obtained at step (i) comprises        2,2,2,3-tetrafluoropropene (1234yf),        1,1,1,2,2-pentafluoropropane (245cb) and        1,1,1,2-tetrafluoro-2-chloropropane (244bb) such that the molar        ratio of 245cb to 244bb is from 1:1 to 70:1, preferably from        1.5:1 to 65:1.    -   step (i) is carried out with a molar ratio HF:1233xf from 3:1 to        150:1, preferably 4:1 to 70:1, more preferably 5:1 to 50:1.    -   step (i) is carried out at a pressure from 3 to 20 bars,        preferably 5 to 15 bars, more preferably 7 to 10 bars.    -   step (i) is carried out at a temperature of from 200 to 450° C.,        preferably from 300 to 430° C., more preferably from 320 to 420°        C.    -   step (i) is carried out with a contact time from 6 to 100 sec,        preferably from 10 to 80 sec, more preferably from 15 to 50 sec.    -   step (i) is carried out in the presence of O₂ and/or Cl₂.    -   the ratio of O₂ and/or Cl₂ with respect to        2-chloro-3,3,3-trifluoro-1-propene (1233xf) is 0.05 to 15 mole        %, preferably 0.5 to 10 mole %.    -   the step of separating into a first stream and a second stream        is a distillation step.    -   step (i) is carried out in the presence of a polymerization        inhibitor, preferably chosen from the group consisting of        p-methoxyphenol, t-amylphenol, limonene, d,1-limonene, quinones,        hydroquinones, epoxides, amines and mixtures thereof.    -   step (i) is carried out in the presence of a catalyst comprising        Ni—Cr, preferably supported.    -   said catalyst is supported on a support selected from        fluorinated alumina, fluorinated chromia, fluorinated activated        carbon or graphite carbon.    -   step (i) is carried out in the presence of a catalyst which is a        chromium catalyst, supported or unsupported, preferably        unsupported.

said catalyst further comprises a co-catalyst selected from Ni, Co, Zn,Mn or mixtures thereof, preferably nickel, and wherein said co-catalystis preferably present in an amount from about 1-10 wt % of saidfluorination catalyst.

-   -   said fluorination catalyst is activated with a        fluorine-containing compound, preferably hydrogen fluoride, and        preferably at a pressure above 10 bars.    -   the process is continuous.

BRIEF DISCLOSURE OF THE DRAWINGS

FIG. 1 is a scheme representing the possible reactions involved in thepresent invention.

FIG. 2 is a scheme representing the process carried out in theinvention.

FIG. 3 is a scheme representing the process carried out in theinvention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

FIG. 1 provides a scheme of potential reactions involved in the instantprocess. 1233xf undergoes a series of possible reactions. Reaction withHF can lead directly to 1234yf or through an addition reaction to asaturated compound 244bb. This saturated compound can bedehydrochlorinated to give 1234yf. 244bb can also, upon fluorinationwith HF, give 245cb. 1234yf and 245cb form an equilibrium; the inventionis based on this finding. Any 245cb formed can be recycled to the firstreaction zone, whereby the equilibrium is displaced (1234yf being thusprevented from further conversion into 245cb). The 245cb flowrate in therecycling loop (either at the exit of the gas-phase reactor or in thesecond stream back exiting the distillation column and back to thegas-phase reactor) is thus substantially constant. No 245cb build upwill thus take place in the recycling loop. In this instance, 1233xf fedinto the reactor converts mainly into 1234yf since 245cb is alreadypresent in the recycling loop.

FIG. 2 represents the process carried out in the invention. Thegas-phase reactor is fed with 1233xf and HF. The reaction mixtureexiting the reactor comprises HCl, unreacted 1233xf, unreacted HF,1234yf, 245cb and a minor amount of 244bb. This reaction stream isseparated by distillation into a first stream (light products)comprising HCl, 1234yf (possibly with a small amount of HF therebyforming an azeotropic mixture) and minor amounts of 245cb and 1233xf. Asecond, heavier, stream is obtained at the bottom of the distillationcolumn, and comprises HF, 1233xf, 245cb and minor amounts of 244bb. Thelighter fraction containing HCl, 1234yf (with HF) and minor amountsother products is again distillated. The top flow comprises HCl, whilethe bottom flow comprises 1234yf and HF, which can again be separatedusing appropriate known methods. Among known methods is the decantation,which produces an HF rich flow which can be recycled to the gas-phasereactor. This decreases the fluorine content downstream in the process,generating less side-products (e.g. CaF₂ which must be discarded). Thestreams exiting the decantation are treated according to known methods,including washing and scrubbing and distillations.

FIG. 3 represents another embodiment, where HCl is removed in a firststep-before distillation of the organic fluorinated products takesplace. The gas-phase reactor is fed with 1233xf and HF. The reactionmixture exiting the reactor comprises HCl, unreacted 1233xf, unreactedHF, 1234yf, 245cb and a minor amount of 244bb. This reaction stream isseparated by a first distillation into a stream containing mainly HCland another stream containing the other products. This other stream isseparated by distillation into a first stream (light products)comprising 1234yf (possibly with a small amount of HF thereby forming anazeotropic mixture) and minor amounts of 245cb and 1233xf. A second,heavier, stream is obtained at the bottom of the distillation column,and comprises HF, 1233xf, 245cb and minor amounts of 244bb. The lighterfraction containing 1234yf (with HF) and minor amounts other products isobtained at the top of the second distillation tower. This top flow canagain be separated using appropriate known methods. Among known methodsis the decantation, which produces a flow of HF which can be recycled tothe gas-phase reactor. This decreases the fluorine content downstream inthe process, generating less side-products (e.g. CaF₂ which must bediscarded). The streams exiting the decantation are treated according toknown methods, including washing and scrubbing and distillations.

The applicant has found that the stream exiting the gas-phase reactorhas a specific composition, due to the recycling of 245cb. Hence, theinvention provides also a composition containing2,2,2,3-tetrafluoropropene (1234yf), 1,1,1,2,2-pentafluoropropane(245cb) and 1,1,1,2-tetrafluoro-2-chloropropane (244bb) such that themolar ratio of 245cb to 244bb is from 1:1 to 70:1, and the molar ratioof 1234yf:245cb is from 1:5 to 3:1; preferably the molar ratio of 245cbto 244bb is from 1.5:1 to 65:1, and the molar ratio of 1234yf:245cb isfrom 1:4 to 2:1. The composition may also comprise 1233xf, andoptionally other compounds such as unreacted HF and HCl.

The gas phase reaction is carried out in the presence of a fluorinationcatalyst. The reaction is carried out in a single gas-phase reactor.

The level of the conversion and selectivity of the desired product canvary according to the processing conditions. The catalyst can be presentin any suitable form, such as fixed or fluidized bed, preferably in afixed bed. The direction of flow may be downward or upward.

This catalyst is for example a catalyst based on a metal including atransition metal oxide or a derivative or halide or oxyhalide such ametal. Catalysts are e.g. FeCl₃, chromium oxyfluoride, chromium oxides(that can optionally be subject to fluorination treatments), chromiumfluorides, and mixtures thereof. Other possible catalysts are thecatalysts supported on carbon catalysts based on antimony, catalystsbased on aluminum (as AlF₃ and Al₂O₃ and oxyfluoride of alumina andaluminum fluoride).

Generally speaking, catalysts that can be used are chromium oxyfluoride,aluminium fluorure and oxyfluoride, and supported or unsupportedcatalyst containing a metal such as Cr, Ni, Zn, Ti, V, Zr, Mo, Ge, Sn,Pb, Mg. Reference can also be made to the disclosures ofWO-A-2007/079431, at page 7, lines 1-5 and 28-32, EP-A-939071, atparagraph [0022], WO 2008/054781 at page 9 line 22 to page 10 line 34,WO 2008/040969 in claim 1, all incorporated herein by reference.

Prior to its use, the catalyst is subjected to activation with HF athigh pressure, typically above about 10 bars (typically at a pressureabove the pressure used in the gas-phase process), as described in U.S.Pat. No. 7,485,598, incorporated herein by reference.

A preferred embodiment uses a particular catalyst, which is a mixedcatalyst, containing both chromium and nickel. The molar ratio Cr:Ni,with respect to the metallic element is generally between 0.5 and 5, forexample between 0.7 and 2, including close to 1. The catalyst maycontain in weight from 0.5 to 20% chromium and 0.5 to 20% nickel,preferably between 2 and 10% of each metal.

The metal may be present in metallic form or as derivatives, includingoxide, halide or oxyhalide. These derivatives, including halide andhalide oxides, are obtained by activation of the catalytic metal.Although the activation of the metal is not necessary, it is preferred.

The support is preferably made from aluminum. There are several possiblecarriers such as alumina, activated alumina or aluminum derivatives.These derivatives include aluminum halides and halide oxides ofaluminum, for example described in U.S. Pat. No. 4,902,838, or obtainedby the activation process described below.

The catalyst may include chromium and nickel in a non-activated oractivated form, on a support that has been subjected to activation ornot.

Reference can be made to WO 2009/118628, and especially to thedisclosure of the catalyst from page 4, line 30 to page 7, line 16,which is incorporated herein by reference.

According to another embodiment, the process uses a high surface area Crbased catalyst which is preferably unsupported. The catalyst canoptionally contain a low level of one or more co-catalyst such as Co,Zn, Mn, Mg and Ni salt. A preferred co-catalyst is nickel. Anotherpreferred co-catalyst is Zn.

The preferred unsupported chromium catalyst can optionally contain lowlevels of one or more co-catalysts selected from cobalt, nickel, zinc ormanganese, prepared by processes known in the art, such as impregnation,mixed powder and the like. The catalyst can be supported or unsupported.For supported catalyst, the catalyst support can be selected frommaterials known in the art to be compatible with HF at highertemperature and pressure. For example, fluorinated alumina,perfluorinated activated carbon, graphite or fluorinated graphite aresuitable catalyst supports. A preferred chromium catalyst is a highsurface area unsupported chromium oxide catalyst. The catalyst isactivated before use. The catalyst activation typically comprises a highpressure, above 10 bars, procedure wherein the catalyst bed is heated toabout 370-380° C., preferably with a continuous flow of nitrogen, afterwhich a mixture of approximately equal volumes of HF and air or nitrogen(preferably nitrogen) are fed over the catalyst bed. The catalystactivation process can be as described in U.S. Pat. No. 7,485,598,incorporated herein by reference. Other fluorinated organic compoundssuch as CHF₂Cl, CHF₃, CF₃CH₂F, CF₃CH₂Cl and the like can be used foractivation. Typically the high pressure catalyst activation proceduretakes about 18 hours.

The resulted high-pressure activated catalyst has a high surface area,such as from about 20 to about 250 square meters per gram. The fluorinecontent typically varies between about 20 to 25 wt %. The pore volumehas an average value between 0.1 to 0.4 m³/g. Crushing strength istypically between about 8 to 15 kg/g. Percent attrition is typically onaverage between 1 to 5 wt %. Cr^((VI)) level is typically in the rangeof 100 to 300 ppm.

The level of the co-catalyst, when present, can be varied between 1 to10 wt %, preferable between 1 to 5 wt %. Co-catalyst can be added to thecatalyst by processes known in the art such as adsorption from anaqueous or organic solution, followed by solvent evaporation. Thepreferred catalyst in this embodiment is pure chromium oxide with nickelor zinc as a co-catalyst. Alternatively the co-catalyst can bephysically mixed with the catalyst via grinding to produce an intimatemixture. An alternative catalyst is a mixed chromium/nickel catalystsupported on fluorinated alumina. U.S. Pat. No. 5,731,481, incorporatedherein by reference, discloses a method of preparation of thisalternative catalyst which would be activated as described hereinabove.

For example, a catalyst which can be used in the invention can beprepared as follows. A Cr₂O₃ catalyst was activated at 16 bars and 350°C. using HF and nitrogen gas. The chemical and physical properties ofthe resulting catalyst are shown in the table below.

% F Content wt % 22.2 Surface Area m²/g¹ 43.9 Pore Volume m³/g² 0.19Crush Strength kg/g³ 10.6 Cr^(+VI) content ppm 201 % Attrition⁴ 3.9¹Surface area was determined by the BET surface area by MicrometricsASAP 2400 ²Pore volume was evaluated using xylene porosity measurement.³Crush strength was evaluated by applying a specified rate ofcompression, until the integrity of the catalyst is compromised.⁴Percent Attrition was evaluated by using ASTM D-4058-92 Standard testmethod for attrition.

The process of the present invention is preferably run continuously.

The 1233xf fluorination process involves contacting 1233xf with HF inthe reaction zone in a gas phase, under conditions sufficient to convertthe 1233xf to fluorination products comprising unreacted 1233xf, 1234yfand 245cb. Such conditions are given below. In addition, otherco-produced underfluorinated intermediates such as 244bb which may bepresent in minor amounts and unreacted 1233xf which are produced as partof the fluorination reaction are also recycled to the reactor. Therecycle stream contains the heavy fraction of the reaction stream whichhas been separated in the distillation step, and especially theequilibrated 245cb.

Typically, step (i) is carried out with a molar ratio HF:1233xf from 3:1to 150:1, preferably 4:1 to 70:1, more preferably 5:1 to 50:1.

Typically, step (i) is carried out at a pressure from 3 to 20 bars,preferably 5 to 15 bars, more preferably 7 to 10 bars.

Typically, step (i) is carried out at a temperature of from 200 to 450°C., preferably from 300 to 430° C., more preferably from 320 to 420° C.The temperature of the bed can be substantially uniform in the reactoror can be adjusted along the path of the stream, decreasing orincreasing along the direction of flow.

Contact times (catalyst volume divided by the total flow rate ofreactants and co-feeds, adjusted to the operating pressure andtemperature) are typically from 6 to 100 sec, preferably from 10 to 80sec, more preferably from 15 to 50 sec.

An oxygen co-feed or chlorine co-feed can be used to extend the catalystlifetime, typically in an amount of from 0.05 to 15 mole %, preferably0.5 to 10 mole % of oxygen or chlorine per 1230xa. The oxygen can beintroduced as an oxygen-containing gas such as air, pure oxygen, or anoxygen/nitrogen mixture. Chlorine can be introduced as achlorine-containing gas such as pure chlorine, or a chlorine/nitrogenmixture.

A polymerization inhibitor can be used to extend the catalyst life,typically in a concentration of from about 50-1000 ppm, more preferablybetween 100-500 ppm. The polymerization inhibitor can bep-methoxyphenol, t-amylphenol, limonene, d,1-limonene, quinones,hydroquinones, epoxides, amines and mixtures thereof. The preferredpolymerization inhibitor is p-methoxyphenol or t-amylphenol. Theco-feeding of a low level of a polymerization inhibitor can control suchpolymerization of chloroolefins and extend the life of the catalyst asdescribed in U.S. Pat. No. 5,714,651, incorporated herein by reference.

The reactants can be fed to the reactor at the same location, atdifferent locations, or using staged feeding at staged locations alongthe reactor. A preferred feeding system is to blow the gaseous reactantsat the bottom of the reactor. Recycling can be done at the entry of thereactor or at an intermediate stage of the reactor; preferably at theentry of the reactor.

In another embodiment, the reaction stream exiting the gas-phase reactorcan be recycled in part to the reactor, before it is subjected to theseparation into a first, light, stream and a second, heavy stream. Therecycling ratio can be as high as 0.7. This recycling allows dilution of1233xf which is very reactive and avoids polymerisation.

Reactions are implemented in a dedicated reactor for reactions involvinghalogens. Such reactors are known to those skilled in the art and caninclude linings based eg Hastelloy®, Inconel®, Monel® or fluoropolymers.The reactor may also include means of heat exchange, if necessary.

As used herein, percentages are by molar percent unless specifiedotherwise.

The following examples illustrate the invention without limiting it.

EXAMPLES

In the following examples, use is made of a catalyst Ni—Cr/AlF₃ which isobtained as follows. The catalyst used is a mixed catalystnickel/chromium of atomic ratio of Ni/Cr=1, supported on aluminafluoride and is prepared by impregnating solutions of nickel and chromicanhydride (CrO₃). After impregnation and drying, the solid is treated ata temperature between 320° C. and 390° C. in the presence of a mixtureof hydrofluoric acid and nitrogen (concentration by volume of 5 to 10%of this acid in nitrogen). The catalyst bed is placed on a grid weldedto the lower end of reactor. The reactor is equipped with a temperaturemeasurement at three locations along the catalyst bed.

Example 1 Fluorination of 1233xf

150 ml of catalyst Ni—Cr/AlF₃ are introduced into the reactor. Thereactor was fed with 16.4 g/hr of HF and 4.1 g/h 1233xf. The reactiontemperature is 352° C. and atmospheric pressure. HF/1233xf molar ratiois 26.9 and the contact time of 4.9 seconds. The conversion rate is then10.3%. The selectivities (amount of one product divided by the sum ofall the products of reaction, this means without 1233xf) were 71.4% in1234yf, 22.7% in 245cb. Other minor compounds detected are: 244bb,1234ze and 245fa. (outlet gas flow contained 89.13 mol % 1233xf, 7.75mol % 1234yf, 2.47 mol % 245cb and 0.65 mol % others).

Examples 2 to 6 Equilibrium 1234yf/245cb

The fluorination reaction of 1233xf is performed according to example 1described above. The flows of HF and 1233xf are adjusted to obtain amolar ratio HF/1233xf close to 5 but varying contact time: 9.5, 18.8,26.7, 37.9 and 39 seconds. The products that are mainly obtained are1234yf and 245cb (if one excludes the 1233xf, not completely converted).The molar compositions 1234yf and 245cb are summarized in table 1. Itcan be concluded that an equilibrium takes place between 1234yf and245cb.

Contact time 1234yf 245cb (s) (%) (%) Ex. 2 9.5 72.53 27.47 Ex. 3 18.869.13 30.87 Ex. 4 26.7 66.49 33.51 Ex. 5 37.9 66.28 33.72 Ex. 6 39 66.1833.82

Example 7

The fluorination reaction of 1233xf is performed according to theembodiment described in Example 1 with an amount of 60 ml of catalystintroduced into the 60 ml reactor. The 245cb is added to the feed. Theflow of 245cb is 2.1 g/hr, the flow 1233xf is 4.5 g/hr and the flow ofHF is 16.2 g/hr. Hence, 100 mol of 1233xf are used with 47 mol 245cb.HF/1233xf molar ratio is equal to 24.5 and the contact time is equal to4.8 s. Air is continuously added in order to preserve the life of thecatalyst. The amount of oxygen introduced is expressed in molar ratioO₂/(1233xf+245cb) and is equal to 0.5%. The molar composition of gasleaving is analyzed by a gas chromatograph: 60.6% 1233xf, 26.6% 1234yf,12.4% 245cb and some other impurities. (89.08 mol 1233xf; 39.07 mol1234yf; 18.17 mol 245cb and 0.72 mol others).

1-35. (canceled)
 36. A process for preparing 2,2,2,3-tetrafluoropropene(1234yf), comprising: (i) contacting 2-chloro-3,3,3-trifluoro-1-propene(1233xf) with hydrogen fluoride HF in the gas phase in the presence of afluorination catalyst under conditions sufficient to produce a reactionmixture; (ii) separating the reaction mixture into a first streamcomprising HCl and 2,2,2,3-tetrafluoropropene (1234yf), and a secondstream comprising HF, unreacted 2-chloro-3,3,3-trifluoro-1-propene(1233xf), and 1,1,1,2,2-pentafluoropropane (245cb); and (iii) recyclingat least a part of the second stream back to step (i).
 37. The processof claim 36, further comprising separating the first stream into HCl and2,2,2,3-tetrafluoropropene (1234yf).
 38. A process for preparing2,2,2,3-tetrafluoropropene (1234yf), comprising: (i) contacting2-chloro-3,3,3-trifluoro-1-propene (1233xf) with hydrogen fluoride HF inthe gas phase in the presence of a fluorination catalyst underconditions sufficient to produce a reaction mixture; (ii) separating thereaction mixture into HCl and a stream comprising fluorinated products;(iii) separating said stream comprising fluorinated products into afirst stream comprising 2,2,2,3-tetrafluoropropene (1234yf) and a secondstream comprising HF, unreacted 2-chloro-3,3,3-trifluoro-1-propene(1233xf), and 1,1,1,2,2-pentafluoropropane (245cb); and (iv) recyclingat least a part of the second stream back to step (i).
 39. The processof claim 36, wherein the reaction mixture obtained in step (i) comprises2,2,2,3-tetrafluoropropene (1234yf) and 1,1,1,2,2-pentafluoropropane(245cb) in a molar ratio ranging from 1:5 to 3:1.
 40. The process ofclaim 39, wherein the reaction mixture obtained in step (i) comprises2,2,2,3-tetrafluoropropene (1234yf), 1,1,1,2,2-pentafluoropropane(245cb), and 1,1,1,2-tetrafluoro-2-chloropropane (244bb), wherein themolar ratio of 245cb to 244bb ranges from 1:1 to 70:1.
 41. The processof claim 38, wherein the reaction mixture obtained in step (i) comprises2,2,2,3-tetrafluoropropene (1234yf) and 1,1,1,2,2-pentafluoropropane(245cb) in a molar ratio ranging from 1:5 to 3:1.
 42. The process ofclaim 41, wherein the reaction mixture obtained in step (i) comprises2,2,2,3-tetrafluoropropene (1234yf), 1,1,1,2,2-pentafluoropropane(245cb), and 1,1,1,2-tetrafluoro-2-chloropropane (244bb), wherein themolar ratio of 245cb to 244bb ranges from 1:1 to 70:1.
 43. The processof claim 36, wherein the molar ratio of HF to 1233xf in step (i) rangesfrom 3:1 to 150:1.
 44. The process of claim 38, wherein the molar ratioof HF to 1.233xf in step (i) ranges from 3:1 to 150:1.
 45. The processof claim 36, wherein step (i) is carried out at a pressure ranging from3 to 20 bars.
 46. The process of claim 38, wherein step (i) is carriedout at a pressure ranging from 3 to 20 bars.
 47. The process of claim36, wherein step (i) is carried out at a temperature ranging from 200 to450° C.
 48. The process of claim 38, wherein step (i) is carried out ata temperature ranging from 200 to 450° C.
 49. The process of claim 36,wherein step (i) is carried out with a contact time ranging from 6 to100 sec.
 50. The process of claim 38, wherein step (i) is carried outwith a contact time ranging from 6 to 100 sec.
 51. The process of claim36, wherein step (i) is carried out in the presence of O₂ and/or Cl₂.52. The process of claim 51, wherein the ratio of O₂ and/or Cl₂ to2-chloro-3,3,3-trifluoro-1-propene (1233xf) ranges from 0.05 to 15 mole%.
 53. The process of claim 38, wherein step (i) is carried out in thepresence of O₂ and/or Cl₂.
 54. The process of claim 53, wherein theratio of O₂ and/or Cl₂ to 2-chloro-3,3,3-trifluoro-1-propene (1233xf)ranges from 0.05 to 15 mole %.
 55. The process of claim 36, wherein thestep of separating into a first stream and a second stream comprises adistillation step.
 56. The process of claim 38, wherein the step ofseparating into a first stream and a second stream comprises adistillation step.
 57. The process of claim 36, wherein step (i) iscarried out in the presence of a polymerization inhibitor.
 58. Theprocess of claim 57, wherein the polymerization inhibitor comprisesp-methoxyphenol, t-amylphenol, limonene, d,1-limonene, a quinone, ahydroquinone, an epoxide, an amine, or a mixture thereof.
 59. Theprocess of claim 38, wherein step (i) is carried out in the presence ofa polymerization inhibitor.
 60. The process of claim 59, wherein thepolymerization inhibitor comprises p-methoxyphenol, t-amylphenol,limonene, d,1-limonene, a quinone, a hydroquinone, an epoxide, an amine,or a mixture thereof.
 61. The process of claim 36, wherein step (i) iscarried out in the presence of a catalyst comprising Ni—Cr.
 62. Theprocess of claim 38, wherein step (i) is carried out in the presence ofa catalyst comprising Ni—Cr.
 63. The process of claim 36, wherein saidcatalyst is supported on a support comprising fluorinated alumina,fluorinated chromia, fluorinated activated carbon, graphite carbon, or acombination thereof.
 64. The process of claim 38, wherein said catalystis supported on a support comprising fluorinated alumina, fluorinatedchromia, fluorinated activated carbon, graphite carbon, or a combinationthereof.
 65. The process of claim 36, wherein step (i) is carried out inthe presence of a supported or unsupported chromium catalyst.
 66. Theprocess of claim 38, wherein step (i) is carried out in the presence ofa supported or unsupported chromium catalyst.
 67. The process of claim36, wherein said fluorination catalyst comprises a co-catalystcomprising Ni, Co, Zn, Mn, or a mixture thereof.
 68. The process ofclaim 67, wherein the amount of co-catalyst ranges from about wt % ofsaid fluorination catalyst.
 69. The process of claim 38, wherein saidfluorination catalyst comprises a co-catalyst comprising Ni, Co, Zn, Mn,or a mixture thereof.
 70. The process of claim 69, wherein the amount ofco-catalyst ranges from about 1-10 wt % of said fluorination catalyst.71. The process of claim 36, further comprising activating thefluorination catalyst with a fluorine-comprising compound.
 72. Theprocess of claim 38, further comprising activating the fluorinationcatalyst with a fluorine-comprising compound.
 73. The process of claim36, wherein said process is continuous.
 74. The process of claim 38,wherein said process is continuous.